The scroll-type compressor is basically composed of a plurality of compression chambers formed by a fixed volute and an orbiting volute engageable with the fixed volute. The poorly-assembled compression chambers are prone to have gaps responsible for causing the compressed work fluid to leak out badly from the side wall of the scroll piece or the root of volute, thereby undermining seriously the volume efficiency of the compressor. In order to overcome such a deficiency as described above, it is necessary that the elements making up the compressor must be made with precision, and that the locating mechanisms of the fixed and the orbiting scroll members must be improved.
In addition, the scroll compressor is vulnerable to damage by the work fluid containing accidentally a foreign object which is either solid or liquid and can not be compressed. Such a noncompressible object can cause the work fluid to have an excessive pressure in the compression chambers of the scroll compressor, thereby making the compressor vulnerable to damage unless the excessively compressed work fluid is discharged in a timely manner via a gap formed elastically by two scroll members. The solution to the problem described above can be further enhanced by an improvement in the locating mechanisms of two scroll members. The prior art improvements in the locating mechanisms of two scroll members of the scroll compressor are described hereinafter.
As exemplified by the disclosures in the U.S. Pat. Nos. 4,767,293 and 4,877,382, the non-orbiting scroll member is provided in the back thereof with a biasing piece device which is fastened securely with a frame by means of bolts in conjunction with a locating piece. In the meantime, the biasing piece device is locked with the non-orbiting scroll member by another set of bolts. The non-orbiting scroll member is capable of moving axially. The moving distance of the non-orbiting scroll member is regulated by the interval between the planar surface of the frame holding the non-orbiting scroll member and the planar surface of the frame locking the biasing piece device, as well as the rim thickness of the non-orbiting scroll member. When the work fluid in the compression chamber has an abnormal pressure, the axial separation force of the compression chamber is greater than the axial sealing force exerting on the back of the non-orbiting scroll member. As a result, a gap is formed between the orbiting scroll member and the non-orbiting scroll member which must overcome the elastic force of the biasing piece by retreating to the planar surface of the biasing piece, which is pressed by the locating piece and is locked with the frame. The prior art improvements described above are defective in design in that the improvements are attained by means of a number of elements at the expense of manufacturing efficiency and assembly precision.
Another prior art improvement is disclosed in the U.S. Pat. No. 5,102,316. This disclosure deals with the non-orbiting scroll member which is provided in the back thereof with a bushing device which is secured to a frame by means of bolts. The non-orbiting scroll member is capalbe of moving axially in conjunction with the bushing device. The axial displacement amount of the non-orbiting scroll member is determined by the difference between the rim thickness of the non-orbiting scroll member and the height of the bushing device. In the meantime, the bottom of the nut serves as a locating surface. When the work fluid in the compression chamber has an abnormal pressure, the non-orbiting scroll member retreats to the locating surface so as to cause the formation of a gap between the orbiting and the non-orbiting scroll members for discharging the work fluid. This prior art improvement is involved with fewer working elements. However, the non-orbiting scroll member is susceptible to being poorly located or being loosened unless the bushing device, the non-orbiting scroll member and the frame are fastened together with precision. Moreover, an additional work must be done with the bottom of the nut, which serves as the locating surface. As a result, this prior art improvement is relatively expensive.